Technical Abstract:
Since the introduction of herbicide (imidazolinone)-resistant rice cultivars into the southern U.S. in 2002, the land area planted to these cultivars has increased steadily, primarily due to the dramatic improvement in control of red rice. At the same time, however, the rice industry has become increasingly concerned about timely and accurate identification of herbicide-resistant and non-resistant red rice hybrids that may develop in these rice fields. We genotyped numerous weedy red rice and rice entries using 180 fluorescently-labeled SSR markers, dispersed across the rice genome, using a microcapillary automated DNA sequencer. The major rice cultivars grown in the U.S. during the past 100 years and a USDA-ARS collection of Oryza spp. red rice lines (non weedy) obtained from rice growing areas throughout the world were included as baseline standards for genotypic comparisons. Genetic distances among Oryza entries were determined from the proportion of SSR alleles shared by the two entries over all markers. GD data were then subjected to hierarchical cluster analysis. These analyses differentiated (GD > 0) among most rice cultivars, red rice types, putative red rice hybrid derivatives, and known hybrids. Multidimensional scaling (MDS) plots provided visualization of the GD between and among rice, red rice, and crosses, and provided insights as to the confirmation of putative crosses as actual crosses, and the inclusion or exclusion of particular Oryza entries as probable parents of a cross. Ultimately, these findings may enable us to confirm the identity and potential source of suspected red rice types or their hybrid derivatives in contaminated fields or seed lots.